by Matt Gibson
Fusarium wilt is a nasty soil-borne pathogen caused by a fungus called fusarium oxysporum. It is known to take over garden areas quickly, attacking any crop or plant that is in contaminated soil. The nightshade family of plants are highly susceptible to fusarium wilt attacks, and so are hundreds of other plants, flowers, and vegetables.
Once the soil has become contaminated by the invasive fungus, drastic measures have to be taken to kill it, so the best way to attack fusarium wilt is by implementing preventive measures, which will keep it out of your garden from the beginning. However, if fusarium wilt has become a problem in your garden, there are a number of steps you can take to try to kill it off before it spreads, causes more damage, and becomes unmanageable.
What Plants Are At Risk for Fusarium Wilt?
Many different plant species are at risk of being plagued by fusarium wilt. Legumes, sweet potatoes, peppers, tomatoes, melons, crisphead lettuce, eggplant, and other widely grown food crops are at high risk for fusarium wilt attacks. When fusarium wilt attacks banana trees, it is commonly known as Panama disease. All in all, this potential fungal nemesis can threaten several hundred different plant species.
What Happens to Infected Plants?
Plants that are affected by fusarium wilt experience stunted growth as well as a load of other symptoms. A healthy plant with dark green leaves begins to yellow or pale as the infection sets in. Over time, infected plants will wilt, wither away, and eventually die from the disease if action is not taken swiftly.
The fungus starts by working its way into the plant’s root system through the soil. Once inside, it moves in to block the vessels in the cells of the infected plant, cutting off water and nutrients as they are being transported to the plant’s extremities. Sometimes, infected plants seem to be affected deeply during the day and appear to shake off the effects after the sun goes down, but gardeners shouldn’t be fooled. Even if it looks like your plants are fighting back, without help from you, they will soon die, and if you don’t take action to kill the fungus off completely, the soil will still be infected if you try to plant another batch of crops.
Symptoms of the disease don’t often appear until late in the growing season. At first, you may notice older leaves that are lower on the stem of the plant beginning to wilt or turn yellow. As the disease progresses further, younger leaves will also start to show signs of vascular distress. Sometimes, however, only one side of the plant will be affected, while the other side appears completely normal—and even blooms or produces fruit.
Not all infected plants die from fusarium wilt. Some just perform especially poorly when it comes to harvesting. Some tomato plants, for example, will survive the attack but will produce very little usable fruit. The fungal infection targets the vascular tissue within the roots and stems of the plant. You can tell what areas of your plants have been affected the most because dark streaks will appear in the veins of the leaves and stem. The lower stems start to decay and even rot. Root rot is quite prevalent as well, especially in seedlings, as they are too small to fight off the invasive disease.
Fusarium wilt begins and thrives in warm temperatures and does not need a host plant to survive year-round. Once it has a hold on your garden’s soil, the fungus fight is on, and it can be a hard one to win.
Crop rotation may help, as it keeps the fungus from attacking the same species of plants again and again. Planting fusarium-resistant crops is highly beneficial, because the fungus tends to stay away from resistant seedlings long enough to give them a fighting chance.
In the long run, sterilization may be the most effective weapon in fighting the fungus off. Use a bleach solution to clean and sanitize pots and garden tools. Discard or burn infected plant debris and compost material, as it is likely to reinfect your garden if not disposed of properly.
Take Offensive Action Against Fusarium Wilt
One highly effective technique used to kill off fusarium wilt and reclaim valuable planting areas is the process of solarizing the soil in your garden beds. Fusarium wilt thrives best in warm temperatures around the 75- to 80-degree Fahrenheit range. Solarization kills off the fungus by raising that temperature up to an extreme heat level where no fungus can survive.
First, remove all infected plants from the soil, and burn or discard them entirely. Then, simply cover the soil with a black plastic tarp, and let the sun do the rest. The black tarp will superheat the soil underneath the tarp by attracting the sunlight and raising the temperature to the level needed to kill off the fungus entirely. Keep the tarp over the infected areas for a full month to make sure the deed is done.
After or during the solarization process, decontaminate all garden equipment that you plan to continue to use including garden tools, gardening gloves, and anything else that will come anywhere near the soil. Sterilize pots with a bleach solution. Permanently remove all plant debris of infected plants. Do not compost this debris. Burn it, ship it to Tahiti, whatever you like—just get it away from your garden. Following these steps to solarize the problem areas, or the entire lot, is the only surefire way to rid yourself of fusarium wilt.
Another action you can take against fusarium invasions is a product called Actinovate, an organic product that can be used as a soil drench. Actinovate is a pesticide and fungicide that targets diseases that cause leaf blight and root rot using beneficial microbes and bacteria that helps plants colonize their roots and protect foliage from invasive diseases.
The United States Environmental Protection Agency has declared Actinovate safe for both humans and the environment itself. The only drawback to this method is the price. In small amounts, Actinovate is quite affordable, but for soil drenching in a large garden area, using this product could wind up being very expensive.
There are other methods you can try before launching into the full-on solar assault. Some fungicides can be purchased and used to conduct a root or bulb soak. This method is not quite as extreme as the solarization process, but it’s still quite an undertaking.
First, remove all affected plants from the soil completely. Then, follow the fungicide’s instructions, and dilute the fungicide with water in large buckets. Finally, soak any underground parts and roots of your crops in the mixture for the recommended time, then hope for the best.
Decontaminating and thoroughly sanitizing all your garden gear is still essential if you are using this method, as fusarium wilt has a tendency to rear its ugly fungal head again if not completely decimated and defended against. There are very few occasions in life that are more frustrating than seeing your garden suffering from a problem that you have put so much effort into fixing, so be sure to complete the job before attempting to harvest another round of crops.
A Few More Important Tips on Fusarium Wilt
Fusarium wilt is one of the hardest soil contaminants to purge from your garden area, so finding out every tip and trick you can glean from gardeners who have dealt with it before is essential. Take extra care not to damage the roots of seedlings before setting them in the soil. Wounded roots give the fungus an ideal entryway into the plant’s internal system. Nitrate fertilizers are recommended over ammonia-based fertilizers when dealing with fungal issues. The fusarium fungus thrives at 75-80 degrees Fahrenheit, so try to keep your garden cool by using a thick layer of mulch to keep the soil from overheating. Raise the pH level of your soil to pH 6.5 to 7.0 to create a fungus-resistant environment. As water is susceptible to contamination, be sure to flush out hoses before irrigating the garden and avoid flood irrigation.
Above all else, try to stay focused on the problem at hand, and don’t get discouraged if you have to try multiple approaches. Fusarium wilt is tough to decimate once it’s taken its hold on a plot of land, but it’s not impossible. Though not the most cost-effective alternative, you could always use containers and plant above ground for a couple of seasons while you solarize the soil or attempt another remedy. If all else fails, seek the help of professionals to eliminate the problem.
Want to learn more about preventing and treating fusarium wilt?
Britannica covers Fusarium Wilt
Gardening Know How covers How to Control Fusarium Wilt
Houzz hosts discussion forum on Ideas and Steps to Take to Control Fusarium Wilt
Planet Natural Resource Center covers Plant Diseases: Fusarium Wilt
Plant Care Today covers Fusarium Wilt